__LIBC_HIDDEN__
int pthread_mutex_unlock_impl(pthread_mutex_t *mutex)
{
int mvalue, mtype, tid, shared;
if (__unlikely(mutex == NULL))
return EINVAL;
mvalue = mutex->value;
mtype = (mvalue & MUTEX_TYPE_MASK);
shared = (mvalue & MUTEX_SHARED_MASK);
/* Handle common case first */
if (__likely(mtype == MUTEX_TYPE_BITS_NORMAL)) {
_normal_unlock(mutex, shared);
return 0;
}
/* Do we already own this recursive or error-check mutex ? */
tid = __get_thread()->tid;
if ( tid != MUTEX_OWNER_FROM_BITS(mvalue) )
return EPERM;
/* If the counter is > 0, we can simply decrement it atomically.
* Since other threads can mutate the lower state bits (and only the
* lower state bits), use a cmpxchg to do it.
*/
if (!MUTEX_COUNTER_BITS_IS_ZERO(mvalue)) {
for (;;) {
int newval = mvalue - MUTEX_COUNTER_BITS_ONE;
if (__likely(__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0)) {
/* success: we still own the mutex, so no memory barrier */
return 0;
}
/* the value changed, so reload and loop */
mvalue = mutex->value;
}
}
/* the counter is 0, so we're going to unlock the mutex by resetting
* its value to 'unlocked'. We need to perform a swap in order
* to read the current state, which will be 2 if there are waiters
* to awake.
*
* TODO: Change this to __bionic_swap_release when we implement it
* to get rid of the explicit memory barrier below.
*/
ANDROID_MEMBAR_FULL(); /* RELEASE BARRIER */
mvalue = __bionic_swap(mtype | shared | MUTEX_STATE_BITS_UNLOCKED, &mutex->value);
/* Wake one waiting thread, if any */
if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(mvalue)) {
__futex_wake_ex(&mutex->value, shared, 1);
}
return 0;
}
int pthread_mutex_unlock(pthread_mutex_t* mutex_interface) {
#if !defined(__LP64__)
// Some apps depend on being able to pass NULL as a mutex and get EINVAL
// back. Don't need to worry about it for LP64 since the ABI is brand new,
// but keep compatibility for LP32. http://b/19995172.
if (mutex_interface == NULL) {
return EINVAL;
}
#endif
pthread_mutex_internal_t* mutex = __get_internal_mutex(mutex_interface);
uint16_t old_state = atomic_load_explicit(&mutex->state, memory_order_relaxed);
uint16_t mtype = (old_state & MUTEX_TYPE_MASK);
uint16_t shared = (old_state & MUTEX_SHARED_MASK);
// Handle common case first.
if (__predict_true(mtype == MUTEX_TYPE_BITS_NORMAL)) {
__pthread_normal_mutex_unlock(mutex, shared);
return 0;
}
// Do we already own this recursive or error-check mutex?
pid_t tid = __get_thread()->tid;
if ( tid != atomic_load_explicit(&mutex->owner_tid, memory_order_relaxed) ) {
return EPERM;
}
// If the counter is > 0, we can simply decrement it atomically.
// Since other threads can mutate the lower state bits (and only the
// lower state bits), use a compare_exchange loop to do it.
if (!MUTEX_COUNTER_BITS_IS_ZERO(old_state)) {
// We still own the mutex, so a release fence is not needed.
atomic_fetch_sub_explicit(&mutex->state, MUTEX_COUNTER_BITS_ONE, memory_order_relaxed);
return 0;
}
// The counter is 0, so we'are going to unlock the mutex by resetting its
// state to unlocked, we need to perform a atomic_exchange inorder to read
// the current state, which will be locked_contended if there may have waiters
// to awake.
// A release fence is required to make previous stores visible to next
// lock owner threads.
atomic_store_explicit(&mutex->owner_tid, 0, memory_order_relaxed);
const uint16_t unlocked = mtype | shared | MUTEX_STATE_BITS_UNLOCKED;
old_state = atomic_exchange_explicit(&mutex->state, unlocked, memory_order_release);
if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(old_state)) {
__futex_wake_ex(&mutex->state, shared, 1);
}
return 0;
}